Method and apparatus for injection and compression molding

ABSTRACT

An injection and compression molding apparatus and a method include the steps of supplying molten resin by injecting it into a cavity formed by molds and compressing the resin by applying pressure. In consideration of problems with respect to the occurrence of sink marks in molded products and the deterioration in precision which are caused by the escape of resin during compression and a change in the cavity distance between two molds, an injection and compression molding apparatus and a molding method therefor are capable of resolving the problems and stably producing molded products with good productivity. A gate is closed during compression, and a supplemental amount of resin can be injected after the compression step so as to supply the desired amount of resin in the molded article. The rear side of a movable mold can be held by a mechanical fixing mechanism so that no change is produced in the distance between the molds owing to the pressure applied during injection, and resin is supplied by injection while the distance between the molds being maintained. It is thus possible to stably provide molded products with good appearance, dimensional precision and quality with good productivity.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an injection and compression moldingapparatus for plastics and a molding method therefor. In one aspect theinvention relates to an injection and compression molding apparatus forplastics and a molding method therefor in which the feed of molten resininto molds, a pressure apparatus and a molding method therefor areimproved.

2. Description of Related Art

In conventional injection molding operations, since molten resin issupplied into a closed mold cavity through a gate, orientation occurs inthe resin, and strong residual strain remains in a portion adjacent tothe gate owing to the high pressure at the gate. Curvature and twistingtherefore occur in molded products, and physical properties in a portionnear the gate deteriorate. A method of resolving this problem is aninjection and compression (or press) molding method in which moltenresin is supplied by injection into molds which are appropriately openedand which are then closed to effect compression molding. In this method,however, if the molten resin flows backward through the gate duringclamping compression, sinking (sink mark) occurs in a portion of themolded article near the gate, and the weight of the resin in the moldedarticle is reduced, resulting in the deterioration in the stability ofthe properties of the resulting molded products. In order to resolvethis problem during clamping compression, several methods have beenproposed, e.g., a first method of effecting compression after the gatehas been closed (after the resin at the gate has solidified), a secondmethod of closing a supply port (Japanese Patent Laid-Open No.61-22917), a third method of controlling compression pressure (JapanesePatent Laid-Open No. 61-83016) and so on.

In injection and compression molding by the first method, however,compression must be effected after the gate has been closed (the resinat the gate is solidified), and thus compression cannot be properlytimed easily. In addition, if the gate size is reduced in order to speedup the sealing of the gate, injection of the resin requires more time,and products having appropriate sizes are not obtained in some cases. Inthe case of the second method in which the supply port is closed, ifcompression is performed early, the resin flows backwardly, and theclosing of the supply port and compression cannot be easily timedbecause the supply port cannot be easily, completely and rapidly closed.In the third method of controlling compression pressure, since there aremany conditional limitations for preventing any counter flow, it isdifficult to set conditions. The second method and third method alsoinvolve the problem that the presence of a sprue runner makes themethods difficult.

In the second method, mold clamping is stopped or the speed of moldingclamping is reduced during the operation of supplying molten resin intothe cavity, Mold clamping is again started or the speed of mold clampingis increased at the same time as or immediately before the molten resinis completely supplied, and press molding is then performed. However,the second method involves the problem that if a movable platen isprecisely stopped or the speed of movement thereof is reduced during thecourse of movement, the movable platen is moved backwardly or inclinedby the reaction force of the molten resin supplied into the cavity ofthe molds, resulting in a change in a compression margin and theformation of defective molded products. The second method also involvesthe following problems. Since the movement of the movable platen isunstable, i.e., the movable platen can be moved backwardly, orcompression is not effected in a parallel state, molded products cannotbe stably obtained. Since molten resin is supplied to the molds whichare appropriately opened, and the molds are then clamped for compressionmolding, if the closing of the supply port and compression are not welltimed when the supply port is closed, the molten resin can flowbackwardly through the gate during clamping compression. Hence, sinkingoccurs in a portion of the molded article near the gate or the weight ofthe resin in the molded article is reduced, and thus molded productscannot be stably obtained.

In consideration of the aforementioned problems, it is an object of thepresent invention to provide an injection and compression moldingapparatus and a molding method therefor which are capable of stablyproducing molded products having good appearance and dimensionalprecision and high quality with good productivity and having no sinkmark in the portion near the resin supply port.

SUMMARY OF THE INVENTION

In one aspect of the present invention, an injection and compressionmolding apparatus comprises a stationary mold, a movable mold which ismoved by a hydraulic means so as to approach or separate from thestationary mold, an injection mechanism for injecting molten resin intoa cavity formed by the two molds, and a gate opening/closing means whichis provided in the injection passage extending from the injectionmechanism to the cavity.

In a second aspect of the present invention, an injection andcompression molding apparatus comprises a stationary mold, a movablemold which is moved by a hydraulic means so as to approach or separatefrom the stationary mold, an injection mechanism for injecting moltenresin into a cavity formed by the two molds, and a mechanical fixingmechanism which mechanically supports the rear side of the movable moldfor the purpose of restricting the backward movement of the movable moldcaused by injection pressure.

In a third aspect of the invention, an injection and compression moldingapparatus comprises a stationary mold, a movable mold which is moved bya hydraulic means so as to approach or separate from the stationarymold, an injection mechanism for injecting molten resin into a cavityformed by the two molds, a gate opening/closing means provided in theinjection passage extending from the injection mechanism to the cavity,and a mechanical fixing mechanism which mechanically supports the rearside of the movable mold for the purpose of restricting the backwardmovement of the movable mold caused by injection pressure. In this case,the gate opening/closing means is a variable valve capable of changingthe effective sectional area of the passage when the valve is opened.

In addition to the above-described arrangements, mold opening can bedetected by a mold opening detecting means so that mechanicalrestriction can be performed at the starting point of compression, or ameans for detecting an injection capacity can be provided so that asuitable starting time of compression can be obtained.

A method for injection and compression molding in accordance with thepresent invention comprises supplying molten resin by injecting it intoa cavity formed by molds, compressing, cooling and then molding theresin, in which a movable mold is temporarily stopped for the purpose ofsupplying resin by injection at a starting point of compression in thestroke of the movable mold, and the gate passage of an injectionmechanism is closed during the compression stroke.

The gate passage is opened after the compression step so that asupplemental amount of the resin can be supplied by injection. In thiscase, the effective cross sectional area of the gate passage during thesecond injection may be smaller than the effective cross sectional areaduring the initial injection. The position where the movement of themovable mold is restricted is detected by mold position sensors so thatthe movable mold is stopped, and the position where compression isstarted is detected by an injection amount detecting means so thatcompression is started.

In the aforementioned embodiment, the gate valve is opened by the gateopening/closing mechanism at the position where the molds are open apredetermined amount so that the resin is injected therein, and the gateis then closed after injection has been completed. Although the resin iscompressed at the time or before the time injection is completed, sincethe gate is closed by the gate opening/closing mechanism untilcompression is completed, only a small amount of resin escapes owing tothe backward flow, and molding can be thus effected with the occurrenceof a backward flow only in a portion of the cavity very close to theinjection port connected to the gate. In addition, since the rear sideof the movable mold is supported by the mechanical fixing mechanism, thecavity is not opened even by the high pressure applied to the cavityduring injection. It is therefore possible to keep a constant margin tocompress. It is also possible to open the gate at the time thecompression is completed or after that time so as to inject asupplemental amount of resin, close the gate after an appropriatesupplemental amount of resin has been injected and stop the injection.It is therefore possible to supply a supplemental amount of resincorresponding to the amount of resin which escapes during thecompression, and obtain molded products with good appearance anddimensional precision and no sinking. In addition, since the passage canbe changed by the variable resin passage mechanism so that the effectivediameter thereof is reduced when the supplemental amount of resin issupplied, the range of transmission of pressure can be adjusted byappropriately selecting the size of the passage area. Further, sinceinjection pressure is applied only to a portion near the region where abackward flow of resin occurs, the supplemental amount of resin can besupplied without residual strain.

Further, since the movable mold is precisely held by the mechanicalfixing mechanism for preventing the mold from moving backwardly when itreaches a predetermined position, a margin to compress is not changed,and molded products can be stably obtained. A predetermined amount ofmolten resin can be injected and charged into the cavity of the moldsmounted on the movable platen fixed at the starting point of compressionwhere the molds are open a predetermined amount, or the molds can bemoved while being maintained parallel during the charge of resin so thatthe molten resin is uniformly compressed in the molds and uniformlyflows therethrough. It is therefore possible to supply a supplementalamount of the resin corresponding to the amount of compressed resinwhich escapes, and to obtain molded products with no sinking and goodappearance, dimensional precision and texture.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1(a) is a drawing of the configuration of a first embodiment of thepresent invention;

FIG. 1(b) is an enlarged view of a part of FIG. 1;

FIG. 2 is a flowchart of the first embodiment of the present invention;

FIG. 3 is an explanatory view of the resin in a near an injection portin the present invention;

FIG. 4 is a front view of a press molding apparatus in a secondembodiment of the present invention;

FIG. 5 is a drawing of the circuit of the same molding apparatus;

FIG. 6 is a partially enlarged view of an injection unit; and

FIG. 7 is a flowchart of the apparatus in the second embodiment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Embodiments of an injection and compression molding apparatus and amolding method therefor in accordance with the present invention aredescribed in detail below with reference to the drawings. FIG. 1 is adrawing of the configuration of a first embodiment of the presentinvention, and FIG. 2 is a flowchart of the same embodiment. In FIG. 1,to a frame 2 of a compression molding machine 1 is fixed a lift cylinder4 for slidably moving a movable die plate 3 by using the hydraulicpressure supplied from a pump (not shown), a movable mold 5 and astationary mold 7 being mounted on the movable die plate 3 and a table6, respectively. An injection port 8 is formed in the stationary mold 7so that the molten resin 9 from an injection portion 40 in the table 6is injected through the injection port 8 and charged into a cavity 10formed by the two molds 5, 7. The movable die plate 3 is mechanicallyfixed by a mechanical fixing mechanism 20 at a position where the twomolds 5, 7 are placed at a predetermined distance (A). The mechanicalfixing mechanism 20 comprises two compression cylinders 21 forcompressing the resin injected and charged into the cavity 10, two links22 for respectively supporting the compression cylinders 21, two lockcylinders 23 for respectively tilting the links 22, two rods 28, and twoheight adjusters 27 which cause the links 22 and the lock cylinders 23to be respectively fixed to cylinder frames 24 through pins 25, 26 andwhich respectively move (in the direction X) the cylinder frames 24 incorrespondence with the thickness of the molds and the predetermineddistance (A) between the molds 5, 7. The injection portion 40 comprisesan injection mechanism 50, a gate opening/closing mechanism 60, and avariable resin passage mechanism 70. The injection mechanism 50comprising a screw 51, a screw rotating motor 52 and an injectioncylinder 53. Pistons in chambers in the injection cylinder 53 causeslidable movement between screw 51 and injection cylinder 53 so that theresin is ram injected by the forward movement of screw 51. A gate 54between the stationary mold 7 and the injection mechanism 50 is providedwith the gate opening/closing mechanism 60 and the variable resinpassage mechanism 70. The valve 63 of the gate opening/closing mechanism60 is opened and closed by actuating a servo motor 62 on the basis ofthe command from a controller 61. The relative position between thepassage 71 formed in the valve 63 of the variable resin passagemechanism 70 and the gate 54 can be changed so that the effective areaof the passage is determined.

The function of the aforementioned configuration is explained below withreference to FIGS. 1, 2 and 3. In FIGS. 1 and 2, the movable die plate 3is moved to the position where the distance (A) between the two molds 5,7 is a predetermined value by sending pressure to the lift cylinder 4from a pump (not shown) during injection and compression molding (Step81). In this step, although the detection of a position is not shown inFIG. 2, when the lift cylinder 4 and the movable die plate 3 arerespectively moved to predetermined positions, hydraulic pressure issent to the lock cylinders 23 of the mechanical fixing mechanism 20,which is adjusted by the height adjusters 27 so that the predetermineddistance (A) is obtained, whereby the mechanical fixing mechanism 20 istilted from the position shown by broken lines (a) to the position shownby solid lines (b). As a result, the movable die plate 3 is mechanicallyfixed (Step 82). The mechanical fixing is detected by positional sensors(not shown) provided on the pins 25, 26 so that the valve 63 of the gateopening/closing mechanism 60 is opened by actuating the servo motor 62on the basis of the command output from the controller 61 (Step 83). Thehydraulic pressure and the amount of oil in injection cylinder 53 arethen controlled so that a predetermined injection speed and injectionpressure can be obtained, and the screw 51 is slid forwardly so that thedesired amount of resin is injected and charged into the cavity 10 (Step84). During this injection operation, the movable mold 5 has thetendency to open owing to the injection pressure in the cavity 10.However, since the movable mold 5 is mechanically fixed through themovable die plate 3, the set distance (A) between the two molds 5, 7 canbe maintained. A decision is made by detecting the axial position ofscrew 51 as to whether or not a predetermined amount of resin has beeninjected, in the same way as in conventional apparatuses. When apredetermined amount of resin is injected, the valve 63 of the gateopening/closing mechanism 60 is closed by actuating the servo motor 62on the basis of the command from the controller 61 (Step 85). Hydraulicpressure is then sent to the compression cylinder 21 for compressing theresin in the cavity 10, and the movable mold 5 is moved toward thestationary mold 7 as a result of the pressure on the movable die plate 3so that compression molding is effected (Step 86). When a predeterminedtime has passed (Step 87) after the movable mold 5 has reached apredetermined position, the servo motor 62 is actuated on the basis ofthe command from the controller 61 so that the passage 71 of thevariable resin passage mechanism 70 is opened a predetermined amount incorrespondence with the area thereof (Step 88). The effective opening ofthe passage during Step 88 is smaller than that for the injected resinin Step 84 and is preferably 3 to 60%, more preferably 5 to 30% of theeffective passage opening during Step 84. When the passage of thevariable resin passage mechanism 70 is opened, a predeterminedsupplemental amount of resin is injected for the purpose of filling therecess (P) formed in a portion extremely near the injection port 8connected to the gate in which a backward flow of the resin occurs, asshown in FIG. 3, so that the range of transmission of pressure does notextend to other charged portions (Step 89). When a predeterminedsupplemental amount of resin has been charged, the variable resinpassage mechanism 70 is again closed (Step 90), and the resin ismaintained under compression until it is cooled. After cooling,hydraulic pressure is sent to the compression cylinders 21 and the lockcylinders 23 so as to release the mechanical fixing mechanism 20, andthe lift cylinder 4 is then moved so that the molds are separated,whereby a molded product can be withdrawn from the molds.

In the above-described embodiment, although the valve 63 of the gateopening/closing mechanism 60 is actuated closed after a predeterminedinitial amount of resin has been charged in Step 84, the gateopening/closing mechanism 60 can be actuated closed during the time ofthe resin charge motion of the pistons in injection cylinder 53.Similarly, although the resin is molded under compression after thevalve 63 of the gate opening/ closing mechanism 60 has been actuatedclosed in Steps 85, 86, the valve 63 of the gate opening/closingmechanism 60 can be actuated closed after the compression molding of theresin has been initiated. In addition, instead of the passage 71 of thevariable resin passage mechanism 70 being opened after a predeterminedtime has passed in Step 87, the passage 71 can be opened by detectingthe pressure in the cavity 10. The mechanical fixing mechanism is notlimited to the aforementioned embodiment, and links moving in parallelto each other may be employed.

A second embodiment is described below with reference to FIGS. 4 to 7.

FIG. 4 is a drawing of the configuration of a second embodiment of thepresent invention, FIG. 5 is a drawing of the circuit of the sameembodiment, FIG. 6 is an enlarged view of a gate opening/closingmechanism, and FIG. 7 is a flowchart. In FIG. 4, reference numeral 100denotes a press molding apparatus for thermoplastic resin. The pressmolding apparatus 100 comprises four lift guide rods 102, a lift frame103 which is supported by the lift guide rods 102 so as tolongitudinally move, an upper die plate 105 which is supported by fourcompression cylinders 104 contained in the lift frame 103, four catchercases 106 respectivey fixed to the four lift guide rods 102, four lockcylinders 107 respectively contained in the catcher cases 106, four liftcylinders 108 for the lift frame 103, a belt driven by a motor 109a forseparately adjusting the four lift guide rods 102 in the longitudinaldirection, a die plate 110 which engages by screws with height adjusters109 operated through worm gears so as to support the adjusters 109, anda frame 111 on which the die plate 110 is loaded and fixed. A movableplaten 130 comprises the lift frame 103 and the upper die plate 105, afixed platen 140 comprises the die plate 110 and the frame 111, and amechanical fixing apparatus 150 comprises the catcher cases 106, thelock cylinders 107, the lift cylinders 108 and the lift guide rods 102.Each of the lock cylinders 107 is provided with a lock detector such asa position sensor 171 or the like for detecting whether or not themovable platen 130 is mechanically locked by the mechanical fixingapparatus 150. An upper mold 112 is fixed to the upper die plate 105,and a lower mold 113 and mold position detectors such as positionsensors 114 are fixed to the die plate 110.

An injection unit 200 comprises an injection mechanism 210, a gateopening/closing mechanism 220, a variable resin passage mechanism 230,and a control section 240, the injection unit 200 being disposed underthe die plate 110.

FIG. 5 is a drawing of the circuit in which the compression cylinders104, the lock cylinders 107 and the lift cylinders 108 are operated bythe hydraulic pressure supplied from a pump 115 through solenoid valves116a, 116b and 116c, respectively. The lock cylinders 107 are operatedby the hydraulic pressure supplied from the pump 115 so as to detect thelocking of the lift frame 103 by the lock detectors such as the positionsensors 171. A flow regulating valve 117 is provided in the circuit ofthe compression cylinders 104 for the purpose of regulating the flowrate in correspondence with the speed detected by the position sensors114 in response to the signal output from a control section 240 so thatthe upper mold 112 is longitudinally moved while being maintainedparallel with the fixed mold 113. This movement controller formaintaining the parallel relationship during movement comprises theposition sensors 114, the flow regulating valve 117, the control section240 and the compression cylinders 104. When the circuits are operated byusing one pump, the circuits can be separately operated with the flowrate being adjusted by the pump, or only one solenoid valve and flowregulating valve can be used to control the four compression cylindercircuits.

The injection mechanism 210 comprises a screw 211, a screw rotatingmotor 212, injection cylinders 213, a flow regulating valve 214, asolenoid valve 215 and a pressure regulating valve 216. The resin iskneaded and measured by using the screw 211 rotated by the screwrotating motor 212. The injection speed of the molten resin iscontrolled by controlling the sliding of the pistons in injectioncylinder 213 by using the flow rate regulated by the flow regulatingvalve 214. The injection output of the molten resin is controlled by thesolenoid valve 216. The amount of resin injected is measured by theposition sensor 217 detecting the position of the pistons in injectioncylinder 213. A gate opening/closing mechanism 220 and the variableresin passage mechanism 230 shown in FIG. 6 are provided in a gateformed between the lower mold 113 and the injection mechanism 210. Thevalve 222 of the gate opening/closing mechanism 220 is opened and closedby operating a servo motor 241 on the basis of the command output fromthe control section 240. The effective area of the passage through valve222 is determined by changing the relative position between the gate 22and the passage 231 formed in the valve 222 of the variable resinpassage mechanism 230.

The operation of the aforementioned structure is described below.

A description is first made of setting of a compression stroke of thepress molding device with reference to FIG. 4. The lift frame 103 isplaced at the lowest point (the lift cylinder 108 is placed at shorteststroke end), and the compression cylinders 104 are placed at theshortest stroke end so that the upper mold 112 and the lower mold 113are put into close proximity with each other by the height adjusters109. At the same time, as the height adjusters 109 are capable ofseparately adjusting the heights of the four lift guide rods 102, thetwo molds can be brought into contact with each other. In the contactstate, the lift frame 103 is mechanically locked to the catcher cases106 by the lock cylinders 107 of the mechanical fixing apparatus 150.Hydraulic pressure is then sent to the port 108a of each of the liftcylinders 108 so as to prevent any backlash. The lift frame 103 is thenmoved upwardly over a required compression stroke by the heightadjusters 109 from the lowest position which is the starting point.During this operation, since the heights of the lift guide rods 102 canbe separately adjusted by the height adjusters 109, the initialparallelism of the upper and lower molds is maintained. The position,which is set in the lock detectors such as the position sensors so thateach of the lock cylinders 107 is mechanically fixed, is input to thecontrol section 240, and the upper mold 112 is stopped at this position,and the melted resin is then injected and charged.

When the molding operation is started, the lock cylinders 107 arereleased in the initial state as shown in FIG. 4, and hydraulic pressureis sent to the port 108b of each of the lift cylinders 108 so as to liftthe lift frame 103 in a state wherein the compression cylinders 104 areat the shortest stroke end. When the molds are closed during compressionmolding in the next step in the flowchart shown in FIG. 7, the liftcylinders 108 are placed at the shortest stroke end, and detection ismade by the mold position detectors as to whether or not the upper moldis lowered to a predetermined position (Step 301). If the upper mold isnot lowered to the predetermined position, the operation in Step 301 isrepeated, and if the upper mold is lowered to the predeterminedposition, a signal is sent to the solenoid valve 116b from the controlsection 240 so as to apply hydraulic pressure to the lock cylinders 107for mechanically locking the lift frame 103 (Step 303). A signal is sentto the control section 240 from each of the lock detectors mechanicallylocked. When the control section 240 receives these signals, it actuatesthe servo motor 241 so as to open the valve 222 of the gateopening/closing mechanism 220 (Step 304). The hydraulic pressure and theamount of oil in the injection cylinder 213 is then controlled by thecontrol section 240 so that the melted resin measured in the injectionmechanism 210 is injected at an injection speed and an injectionpressure which are previously set, and a predetermined amount of theresin is injected and charged into the cavity by the screw 211 (Step305). During this operation, although the upper mold 112 tends to openowing to the reaction force caused by the pressure of the resin in thecavity, a predetermined set distance between the two molds can be keptbecause the upper mold 112 is mechanically fixed through the lift frame103.

The axial position of the screw 211 can be detected by the positionsensor 217 for making a decision as to whether or not a predeterminedamount of resin has been injected, in the same way as in conventionalapparatuses. If a predetermined amount of resin has been injected, asignal is sent to the control section 240 from the screw positiondetector, and when the control section 240 receives this signal, itsends to the solenoid valve 116a a signal of command to startcompression so that hydraulic pressure is sent to the compressioncylinders 104 from the pump 115, whereby the resin in the molds iscompressed (Step 306).

In this step, the position of the upper mold is detected by the moldposition detectors, which are respectively provided at the four cornersof the die plate 110, and the detection signal is sent to the controlsection 240 in which the speed is calculated (Step 304). On the basis ofthis signal, the amount of oil sent to the compression cylinder 104 iscontrolled by the flow regulating valve 117 on the basis of the commandfrom the control section 240 so that the upper mold is lowered whilebeing maintained parallel with the lower mold (Steps 308, 309). Duringcompression molding, when the screw position detector detects that apredetermined amount of resin required for a product has been chargedinto the cavity of the molds (Step 310), the control section 240receives the detection signal and then operates the servo motor 241 soas to close the valve 222 of the gate opening/closing mechanism 220(Step 311). Even if the valve 222 is closed so that the supply of theresin is stopped, the compression cylinders 104 are controlled so thatthe upper mold is moved downwardly in parallel with the lower mold inthe same way as that described above.

When the upper mold has been moved to a predetermined position, forexample, at which the two mold are in contact with each other, and whencompression molding has been performed, and then a predetermined timehas passed (Steps 312, 313), the servo motor 241 is actuated on thebasis of the command from the control section 240 so that the passage231 of the variable resin passage mechanism 230 is opened a given amountcorresponding to the area which is previously set (Step 314). At thistime (Step 310), the degree of opening of the passage is smaller thanthat during injection in Step 305, and is preferably 3 to 60%, morepreferably 5 to 30% of the effective opening during Step 305. When thepassage 231 of the variable resin passage mechanism 230 is opened, apredetermined supplemental amount of resin is injected for the purposeof filling the recess formed in a portion near the injection portconnected to the gate where a backward flow of the resin occurred sothat the range of transmission of pressure does not extend to otherregions charged with the resin (Step 315). When a predeterminedsupplemental amount of resin is charged, the variable resin passagemechanism 230 is again closed (Step 316), and the resin is maintained inthe molds until it is cooled. After cooling, hydraulic pressure is sentto the compression cylinders 104 and the lock cylinders 107 so as torelease the mechanical fixing mechanisms 150, whereby the molds can beopened after the lift cylinder has been moved and the molded product canbe withdrawn from the molds.

In the aforementioned embodiment, although backlash is removed bylocking the lift frame 103 by the lock cylinders 107 and applyinghydraulic pressure to the ports 108a, backlash may be removed before orafter locking. In addition, although the position sensors detect themovement of the movable mold for the purpose of maintaining the movablemold parallel with the fixed mold during movement of the movable mold,the movement may be detected by using the upper die plate, the rod ofthe compression cylinder or the like.

Further, although the upper and lower molds can be put into contact witheach other during setting of the compression stroke, in the case ofknown dimensions the height adjusters 109 can be separately adjusted sothat the initial parallelism is maintained. The resin compressionmolding can be performed by moving the movable mold downwardly whilecharging the resin, or compression molding can be effected after theresin has been charged and the valve has been closed. In addition, amargin to compress between the two molds can be controlled by the heightadjusters, or the margin can be controlled by using hydraulic cylinderssuch as the lift cylinders or the like.

As described above, each of the above-described embodiments enables thesupply of a supplemental amount of resin corresponding to the amount ofthe compressed resin which escaped. The embodiments also have theeffects that, since the area of the passage can be set to a small valueand changed by the variable resin passage mechanism, the range oftransmission of pressure can be adjusted by selecting the area of thepassage and the injection pressure can be applied only to a portion ofthe resin in the mold cavity near the region where a backward flow ofthe resin occurs. It is therefore possible to provide an injection andcompression molding apparatus and a molding method therefor which iscapable of stably producing molding products having good appearance,dimensional precision and quality with good productivity.

An injection and compression molding apparatus and a molding methodtherefor in accordance with the present invention can be applied tomolding apparatuses in which resin is molded by injection andcompression in various kinds of industry of manufacturing plastic moldedproducts.

What is claimed is:
 1. In an injection and compression molding methodwherein a first mold is moved towards a second mold, the movement ofsaid first mold toward said second mold is temporarily stopped at aboutthe starting position of compression so that an initial amount of moltenresin can be supplied by injection through a gate passageway into acavity formed by said first and second molds, said gate passageway intosaid cavity is closed upon said initial amount of molten resin beingsupplied through said gate passageway into said cavity, the first moldis moved from its stopped position towards said second mold to initiatethe compression molding of the resin in said cavity, and the thuscompressed resin is cooled to form a molded article, the improvementcomprising opening said gate passageway and injecting a supplementalamount of molten resin through said gate passageway into said cavityafter the initial amount of molten resin has been compressed, to therebyprovide the desired amount of resin in the molded article.
 2. Aninjection and compression molding method in accordance with claim 1,wherein the effective cross sectional area of the gate passageway issmaller during the injection of said supplemental amount than during theinjection of said initial amount.
 3. An injection and compressionmolding method in accordance with claim 1, further comprisingestablishing a signal when said first mold is at a predeterminedposition, and wherein said first mold is stopped, at about the startingposition of compression, by lift cylinders driven on the basis of saidsignal.
 4. An injection and compression molding method in accordancewith claim 1, further comprising generating a signal when the injectionof a predetermined amount of molten resin into said cavity is completed,and wherein the step of moving said first mold from its stopped positiontowards said second mold is started on the basis of said signal.
 5. Aninjection and compression molding method in accordance with claim 1,wherein the effective cross section al area of the gate passagewayduring the injection of said supplemental amount is in the range of 3 to60 percent of the effective cross sectional area of the gate passagewayduring the injection of said initial amount.
 6. An injection andcompression molding method in accordance with claim 1, wherein theeffective cross sectional area of the gate passageway during theinjection of said supplemental amount is in the range of 5 to 30 percentof the effective cross sectional area of the gate passageway during theinjection of said initial amount.
 7. An injection and compressionmolding method in accordance with claim 1, wherein the closing of saidgate passageway upon said initial amount of molten resin being suppliedthrough said gate passageway into said cavity is performed after thecompression molding of the resin contained in said cavity has beeninitiated and prior to the step of opening said gate passageway for theinjection of said supplemental amount of molten resin.
 8. An injectionand compression molding method in accordance with claim 1, wherein saidgate passageway contains a variable gage valve, wherein said gate valveis opened to provide a first effective cross section of the gatepassageway for permitting said initial amount of molten resin to besupplied through said gate passageway into said cavity while said firstmold is temporarily stopped at about the starting position ofcompression, wherein said gate valve is closed after said initial amountof molten resin has been supplied to said cavity, wherein after saidinitial amount of molten resin has been compressed said gate valve isopened to provide a second effective cross section of the gatepassageway for permitting said supplemental amount of molten resin to beinjected through said gate passageway into said cavity, and wherein saidsecond effective cross section is smaller than said first effectivecross section.
 9. An injection and compression molding method inaccordance with claim 8, wherein said second effective cross section isin the range of 3 to 60 percent of said first effective cross section.10. An injection and compression molding method in accordance with claim8, wherein said gate valve is opened to provide said second effectivecross section of the gate passageway at a predetermined time after saidinitial amount of molten resin has been compressed.
 11. An injection andcompression molding method in accordance with claim 8, wherein said gatevalve is opened to provide said second effective cross section of thegate passageway in response to the detection of a predetermined pressurein said cavity.
 12. An injection and compression molding apparatuscomprising a compression molding apparatus for opening and closing amovable mold and a stationary mold, an injection apparatus for supplyingmolten resin to at least one cavity formed by said movable andstationary molds, mold position detecting means for detecting apredetermined position of said movable mold wherein said movable andstationary molds are open, mechanical fixing means for mechanicallyfixing said movable mold at said predetermined position, gate means forpermitting molten resin from said injection apparatus to flow through aresin passageway into said at least one cavity when said mold positiondetecting means detects said predetermined position and said movablemold is mechanically fixed in said predetermined position, injectionamount detecting means for detecting that an initial predeterminedamount of molten resin has flowed into said at least one cavity, andcompression means for moving said movable mold from said predeterminedposition towards said stationary mold to compress the initialpredetermined amount of molten resin contained in said at least onecavity, wherein said gate means comprises a variable position gate valvelocated in the resin passageway to said at least one cavity and a gatecontrol means for closing said gage valve and for varying the positionof said gate valve when it is open to thereby change the effective crosssection of the resin passageway when said gate valve is open, whereinsaid gate control means comprises means for opening said gate valve toprovide a first effective cross section of the resin passageway forpermitting molten resin from said injection apparatus to flow into saidat least one cavity when said mold position detecting means detects saidpredetermined position and said movable mold is mechanically fixed insaid predetermined position, for closing said gate valve when saidinjection amount detecting means has detected that the initialpredetermined amount of molten resin has flowed into said at least onecavity to thereby stop the flow of molten resin into said at least onecavity after said initial predetermined amount of resin has flowed intosaid at least one cavity, for opening said gate valve to provide asecond effective cross section of the resin passageway for permitting asupplemental amount of molten resin from said injection apparatus toflow into said at least one cavity after said compression means hasmoved said movable mold from said predetermined position into contactwith said stationary mold to compress the initial predetermined amountof molten resin, and for closing said gate valve when said supplementalamount of molten resin has flowed into said at least one cavity, saidsecond effective cross section being smaller than said first effectivecross section.
 13. An injection and compression molding apparatus inaccordance with claim 12, wherein said second effective cross section isin the range of 3 to 60 percent of said first effective cross section.14. An injection and compression molding apparatus in accordance withclaim 12, wherein said gate control means opens said gate valve toprovide said second effective cross section of the resin passageway at apredetermined time after said compression means has moved said movablemold from said predetermined position into contact with said stationarymold to compress the initial predetermined amount of molten resin. 15.An injection and compression molding apparatus in accordance with claim12, wherein said gate control means opens said gate valve to providesaid second effective cross section of the resin passageway in responseto the detection of a predetermined pressure in said at least onecavity.